1. Field of the Invention
The present invention relates to a single-layer-electrode type two-phase charge coupled device (CCD) and a method for manufacturing the same.
2. Description of the Related Art
Recently, single-layer-electrode type two-phase CCDs have been developed by etching a single conductive layer with a fine Photolithography and etching process to obtain electrodes whose spacing is about 0.2 to 0.3 xcexcm.
In the single-layer-electrode two-phase CCDs, since no overlapping of the electrodes is present, a capacitance between the electrodes can be small and no poor insulation is present between the electrodes. Further, since it is unnecessary to oxidize the electrodes to obtain insulation thereof, the electrodes can be made of metal or silicide in addition to polycrystalline silicon, to further reduce the resistances of the electrodes.
A prior art single-layer-electrode type two-phase CCD includes a semiconductor substrate having a plurality of semiconductor regions, and also, includes a plurality of charge transfer electrodes opposing the semiconductor regions. This will be explained later in detail.
In the above-mentioned prior art CCD, however, the semiconductor regions are not in self-alignment with the charge transfer electrodes. As a result, if the semiconductor regions are shifted in the outside or inside direction with respect to the charge transfer electrodes, potential protrusions or potential recesses appear in the potential within the CCD. The potential protrusions and potential recesses reduce the efficiency of charge transfer.
It is an object of the present invention to provide a single-layer-electrode type two-phase CCD capable of smooth charge transfer.
According to the present invention, in a charge coupled device, trap levels formed by insulating layers or floating electrodes are formed on a semiconductor layer (or a semiconductor substrate). Stationary charges are trapped in some of the trap levels or floating electrodes. The charge transfer electrodes are in self-alignment with potential barrier regions.
Thus, potential protrusions or potential recesses within the CCD are dissolved to enhance the charge transfer efficiency.